The present invention relates to an apparatus for the spray treatment of printed circuit boards in the course of the printed circuit board (PCB) production, having means of conveyance for conveying the PCBs with a horizontally oriented PCB surface plane, also a nozzle device disposed above the plane of conveyance of the PCBs for spraying the top surface of the PCBs with a liquid treatment medium stored in a reservoir, and a suction device for suctioning off the sprayed-on treatment medium from the top surface of the PCBs during the spray process.
A treatment apparatus of the above type becomes apparent from DE 41 21 032 A1. It is used, for example, in the etching treatment of PCBs within the framework of the PCB production. A problem in the production of PCBs generally lies in the fact that the treatment fluid that is sprayed from above onto the horizontally conveyed PCBs does not drain quickly enough, with the result that the fluid may back up, which can result in an uneven treatment and possibly even in damage to the PCBs. To counter this problem, in the known apparatus the PCBs being treated are subjected from above simultaneously to a spray process and a suction process. While passing through the apparatus, the PCBs are sprayed with the desired liquid treatment medium, for example with an etching, developing or rinsing fluid; and a suction process, within the framework of which the sprayed-on liquid is directly suctioned off from the top surface of the PCB, takes place parallel to the spray process. In this manner a backing up of fluid is prevented and the PCBs are also very effectively freed from residual fluid even if apparatus components are present that interfere with a normal draining of the liquid. The suction device, as a rule, cannot remove the entire sprayed-on treatment medium, of course. However, the suction intensity can be selected such that the effect of the resulting inevitable fluid removal has a very positive influence on the treatment result.
The suction effect in the known treatment apparatus is created by a vacuum pump, which has a preceding container that serves to separate suctioned off liquid fractions and air fractions. The air is drawn off and the separated treatment medium is carried back into the reservoir to be available for a new spray treatment.
Separating the air from the treatment medium within the suction branch requires a very complex and expensive layout. The same applies for the steps to filter out the separated air, which is released into the environment.
From DE 198 30 212 A1 an apparatus is known for treating objects, for example PCBs, wherein the objects being treated are fed translationally to a treatment bath and rotated in the treatment bath. A suction device permits fluid that adheres to the objects to be suctioned off. The negative pressure required for this can be generated with suitable sets of equipment, especially with water-jet pumps.
The present invention has as its object to reduce the layout complexity and expense connected with the suction measures while maintaining a high-quality and even treatment process for the PCBs.
This object is met with a circulation cycle that is provided with a circulating pump and incorporates an ejector device that is fed with treatment medium through the circulating pump and on the suction side of which the negative pressure, which is required for the suction operation, is tapped off.
In this manner the negative pressure that is required for the suction can be generated in a closed cycle within the treatment apparatus itself Within the ejector device the circulated treatment medium serves to generate the desired suction effect so that neither a separation of air and treatment medium becomes necessary nor expensive filtering measures to filter out the air. The technical complexity and, hence, also the expenditure can accordingly be kept low while attaining a very high suction performance.
Advantageous improvements of the invention will become apparent from the subclaims.
The nozzle device is advantageously designed such that it defines at least one spray zone in such a way that the spray zone has corresponding preceding and succeeding suction zones of the suction device relative to the direction of conveyance. The suction result is optimal if both a suction zone that precedes the given spray zone and a suction zone that succeeds it exist, because the sprayed-on treatment medium is, in this case, suctioned off reliably both at the front and the back and no dust is generated.
Particularly advantageous is an embodiment in which a plurality of successive, spaced-apart spray zones, each of which are flanked by a preceding and a succeeding suction zone, are provided in the direction of conveyance of the PCBs.
The suction device is designed especially in such a way that it develops its suction effect across the entire width of the PCB.
The suction device preferably has a suction nozzle arrangement that is placed immediately above the plane of conveyance of the PCBs and advantageously incorporates at least one suction nozzle unit consisting of one or multiple suction nozzles that extend crosswise to the plane of conveyance. In a solution with a particularly simple design the suction nozzle units are formed by suction tubes that are provided with one or more slit-like openings, which constitute the suction nozzles.
The means of conveyance for the PCBs advantageously have lower conveyor rollers on which the PCBs are moved along during the spraying and suction process. Upper conveyor rollers may additionally be provided that act upon the top surface of the PCBs to ensure an exact guiding and optionally also to hold them securely in place relative to the suction effect from above. The upper conveyor rollers may be vertically movable to attain an automatic adjustment to the thickness of the given PCB.
If the suction device is designed such that it is effective in only one or advantageously in multiple suction zones that are spaced apart in the direction of conveyance, a suction nozzle unit, e.g., a suction tube, that extends crosswise to the direction of conveyance and has both preceding and succeeding conveyor rollers, may be provided in at least one and preferably in each suction zone. The possibility exists to combine a given suction nozzle unit together with the adjacent upper conveyor rollers into a separately operable suction unit that can be installed or exchanged independently from other suction units.
The conveyor rollers may, for example, be formed by individual rollers that are spaced apart with the same rotation axes, however, a cylinder-like design, for example, would be possible as well.